`babel-plugin-macros` should be an optional peer dependency

[G-Rath]

While I've not used macros myself, from what I can tell dedent/macro.js is only expected to be used when babel-plugin-marcos is being used and is a special file that is consumed by the plugin (i.e. even if I'm using babel-plugin-macros, I still myself wouldn't write require('dedent/macros.js')).

As such, I think it's safe to list it as an optional peer dependency so that folks who are not using the macro don't have to carry around this extra dependency.

[JoshuaKGoldberg]

#60 is released as dedent@1.2.0 👍